function findMissingNumber(sequence) {
  //your code here
  let array = sequence.split(' ').sort(function (a, b) { return b - a });
  let result = 0;
  if (sequence.length == 0){
    result = 0;
  } else if (array[array.length-1] != 1) {
    result = 1;
  } else {
      for (var i = 0; i < array.length-1 ; i++) {
        let difference = array[i] - array[i+1];
        if (!array.some(isNaN)) {
          if (difference == 1){
          result = 0;
          } else if (difference == 2){
            result = parseInt(array[i]) - 1;
            break;
          } else {
            result = (parseInt(array[i+1]) + 1);
            break;
          }
        }else {
          result = 1;
          break;
        }
    }
  }

  return result;
}